P1249: INSUFFICIENT PPARΔ IN BONE MARROW ENDOTHELIAL PROGENITOR CELLS LEADS TO THEIR IMPAIRED HEMATOPOIESIS-SUPPORTING ABILITY
Authors: MI Liang, Wei-LI Yao, Zhong-Shi Lyv, Shu-Qian Tang, Tong Xing, Yuan-Yuan Zhang, Yu-Hong Chen, Yu Wang, Lan-Ping Xu, Xiao-Hui Zhang, Xiao-Jun Huang, Yuan Kong
Journal: HemaSphere (2023)

Topic: 21. Stem cell transplantation - Experimental Background: Poor graft function (PGF), characterized by pancytopenia, is a severe complication following allogeneic hematopoietic stem cell transplantation (allo-HSCT). Our prior works (BBMT 2013; BMT 2016; Blood 2016; Haematologica 2022) reported that the decreased and dysfunctional bone marrow (BM) endothelial progenitor cells (EPCs), a crucial cellular component in moderating hematopoietic stem cells (HSCs) in the BM microenvironment, were implicated in the pathogenesis of PGF. Moreover, prophylactic approaches to rescue aberrant BM EPCs in PGF patients could promote hematopoietic reconstitution after allo-HSCT (Blood Advances 2019; BMC Med 2022), further confirming the vital role of BM EPCs in regulating hematopoietic recovery post-allo-HSCT. However, the underlying mechanism by which EPCs mediate HSCs remains to be elucidated. Peroxisome proliferator-activated receptors (PPARs), consisting of three isotypes, PPARα, PPARγ and PPARδ, act as key members of the nuclear receptor superfamily of transcription factors that govern a variety of biological processes, such as cell metabolism, proliferation, differentiation and survival. Recently, PPARδ, but not PPARα or PPARγ, was reported to be the predominant expressed isotype of PPARs in BM HSCs and plays a critical role in regulating HSC activities, including maintenance of stemness and asymmetric division. Although PPARδ plays an essential role in HSCs, its effect on BM EPCs, the indispensable niche for HSCs, is largely unknown. Aims: To determine the effects of PPARδ on regulating the function of BM EPCs. Furthermore, to investigate the role of PPARδ in BM EPCs of PGF patients, and the therapeutical potential of PPARδ-targeted drugs to the dysfunctional BM EPCs derived from PGF patients post-allotransplant. Methods: PPARδ knockdown, overexpression and RNA sequencing were performed in BM EPCs derived from healthy donors (HDs). Additionally, a prospective case‒control study enrolled 10 patients with PGF, 10 matched patients with good graft function (GGF), was further conducted to investigate the intracellular levels of PPARδ in BM EPCs. Furthermore, GW501516, an agonist of PPARδ, was added to the cultivated BM EPCs derived from PGF patients. The functions of cultivated BM EPCs were evaluated by migration, the immunofluorescent staining of DiI-AcLDL and UEA-I, tube formation, apoptosis and colony-forming unit (CFU) assays. Results: PPARδ knockdown significantly reduced the number and impaired the function of cultivated BM EPCs derived from HDs, characterized by increased levels of apoptosis and decreased abilities of migration, tube formation and hematopoiesis-supporting ability. PPARδ overexpression restored the abovementioned EPC dysfunction induced by PPARδ knockdown. Mechanistically, RNA sequencing showed that PPARδ knockdown enhanced the reactive oxygen species pathway and decreased the protein secretion pathway and cytokine‒cytokine receptor interaction, which is consistent with the impaired hematopoiesis-supporting ability of BM EPCs with PPARδ silencing. There was decreased expression of PPARδ in BM EPCs of patients with PGF compared with patients with GGF. Furthermore, GW501516 could benefit BM EPCs derived from patients with PGF, especially enhancing their ability to support hematopoiesis in vitro. Summary/Conclusion: Our results suggest that PPARδ promotes the hematopoiesis-supporting ability of human BM EPCs. Defective PPARδ in BM EPCs may be involved in the pathogenesis of PGF, whereas the hampered hematopoiesis-supporting ability of BM EPCs of PGF patients could be attenuated by the agonist of PPARδ (GW501516) in vitro. Our findings may provide a promising therapeutic approach for patients with PGF post-allo-HSCT. Keywords: Hematopoiesis, Bone marrow microenvironment, Allogeneic hematopoietic stem cell transplant, Endothelial progenitor cell